In recent years, it has been a mainstream to mount camera modules in information terminals mainly exemplified by cellular phones. These camera modules have been required to have a simple structure enabling manual changeover between conventional two of tele and macro focal points, and also to be highly functional with the auto-focus function, the zoom function, or the like. In order to incorporate the auto focus function or the zoom function into such a camera module, there is required an actuator for moving a plurality of lenses along an optical axis with respect to an image pickup unit (such as a CCD or a CMOS), and therefore researches and developments have been made on various types of actuators.
On the other hand, such actuators for use in moving a group of lenses are required to have light weights and small sizes, along with the reduction in the sizes of information terminals. Further, these actuators are required to consume less power than the electric power necessary for main functions of the information terminals which incorporate the actuators.
Therefore, studies have been conducted, regarding the practical utility of polymer actuators as actuators which consume less power. The use of polymer actuators eliminates the necessity of components such as gears for providing operations such as linear movement and bending, and also enables extraction of outputs with a simple structure, since the actuators themselves can deform.
Non Patent Document 1 discloses a case where ion conduction actuators, which are polymer actuators of one type, are applied to drive lenses in an auto-focus camera module. This auto-focus camera module is constituted by a lens bracket housing the ion conduction actuators, an electrode plate for applying a voltage to the ion conduction actuators, and a group of lenses; an actuator fixing spring; and a case.
The group of lenses is moved along an optical axis by applying a voltage to the ion conduction actuators 110 through electrode, bending the arm-shaped portions of the actuators 110 and pushing a flange-shaped portion 111a of the lens bracket 111 upwardly, as illustrated in FIG. 57A and FIG. 57B. In this case, movement of the group of lenses along the optical axis is restricted by the outer cylindrical portion of the lens bracket 111 and the inner diameter of the case. In this case, the case is not illustrated. However, the ion conduction actuators 110 recede by δx within a plane intersecting with the direction of the optical axis, when they are bent and displaced by δz through application of a voltage thereto, as illustrated in FIG. 57C. Therefore, when the lens bracket 111 is moved along the optical axis, this induces gaps between the lens bracket 111 and the arm-shaped portions of the ion conduction actuators 110. When the auto focus camera module is used in a state of being along the horizontal direction or being inclined, the gaps induce a clearance between the lens bracket 111 and the case, and this clearance induces the issue of an inclination with respect to the optical axis of the group of lenses and the image pickup device portion.
Patent Document 1 discloses another example where a polymer actuator is applied to a lens driving mechanism. As illustrated in FIG. 58 (see FIG. 5 in Patent Document 1), the lens driving mechanism brings a tongue piece 251 formed along the circumferential direction into contact with an end surface of a lens frame 230, which deforms the tongue piece 251 for moving the lens frame 230. With this structure, the thickness of the actuator portion is added to the thickness of the lens frame 230 along the optical axis, thereby inducing the issue of increase of the thickness of the lens driving mechanism along the optical axis. Further, this structure is adapted to slide the lens frame 230 against the inner surface of the mirror tube such that the lens frame 230 moves along the optical axis, thereby inducing the issue that smooth operations become unstable due to influence of the friction.
Patent Document 2 discloses another example where a polymer actuator is applied to an optical device. As illustrated in FIG. 59 (see FIG. 1 in Patent Document 2), there is disclosed a structure which secures a plurality of actuators 501 corresponding to tongue pieces to a lens frame 300. Further, there is disclosed a method for adjusting the inclination of the lens frame 300 or adjusting the eccentricity of the lens frame 300 by displacing the plurality of actuators 501 individually. In cases where this structure is applied to an auto-focus lens holder driving device, when there are variations in amount of deformation among the plurality of actuators 501 or when some of the actuators 501 are failed to be inoperable, there is induced the issue of an inclination of the lens frame 300.
Patent Document 1: Japanese Unexamined Patent Publication No. 2007-139862
Patent Document 2: Japanese Unexamined Patent Publication No. 2007-286320
Non Patent Document 1: “Development of Polymer Actuators and Applications thereof”, Journal of The Japan Society of Mechanical Engineers (Kazuo Onishi, March 2007 Vol. 110 No. 1060 p 172-173).